TrueCrypt is a source-available freeware application used for on-the-fly encryption (OTFE). It can create a virtual encrypted disk within a file or encrypt a partition.

TrueCrypt is a free open source on-the-fly encryption (OTFE) program for Microsoft Windows XP/2000/2003/Vista and Linux. It allows one to create a virtual encrypted disk (TrueCrypt volume) within a file and then mount it as a real disk. TrueCrypt can also encrypt an entire hard disk partition or a storage device/medium, such as floppy disk or USB memory stick. Thus, TrueCrypt creates device-hosted TrueCrypt volumes. Everything stored on a TrueCrypt volume is entirely encrypted (i.e., including file names and folder names). TrueCrypt volumes behave as real physical disk drives. This means that it is possible, for example, to repair the encrypted filesystem with chkdsk, defragment mounted volumes created by TrueCrypt, etc.

TrueCrypt Features

Creates a virtual encrypted disk within a file and mounts it as a real disk.

Encrypts an entire hard disk partition or a storage device such as USB flash drive.

Encryption is automatic, real-time (on-the-fly) and transparent.

Provides two levels of plausible deniability, in case an adversary forces you to reveal the password.